1. Field of the Invention
The present invention relates generally to a nuclear reactor water cleanup pump and, more particularly, is concerned with a method and a means for internally cooling the nuclear reactor cleanup pump of a boiling water reactor.
2. Description of the Prior Art
In boiling water nuclear power plants, a reactor coolant system is used to transport heat from a reactor core to steam generators for the production of steam. The steam is then used to drive a turbine generator. During the process, a substantial amount of mineral deposits are formed in the reactant coolant, which necessitates "cleanup" of the coolant. A coolant recirculation system is utilized whereby cleanup pumps transport the reactant coolant from the reactor to a demineralizer from where the reactant coolant is delivered back into the reactor.
The reactor cleanup pump generally has a "canned" motor which is totally contained and requires little maintenance. A purge fluid system is generally provided for forcing any mineral deposits in the pump out of the canned motor and bearings during start-up, hot-standby, and/or shut-down operations of the pump. The temperature of the reactor coolant water is typically in the range of from approximately 500.degree. to 600.degree. F. which is too hot to also use to cool the motor and bearings of the cleanup pump. Thus, a heat removal system separate from, and which does not employ the reactor coolant water has been generally utilized in the prior art. One type of heat removal system is a heat exchanger which is comprised of an annular hollow jacket surrounding the motor and a set of coils contained in the jacket and surrounding the motor. Other sets of coils may be located adjacent to the upper and/or the lower beatings. The multiple sets of coils are connected in flow communication so as to define a closed path for circulation of an internal coolant fluid therein for cooling the bearings and the motor.
The annular jacket of the heat removal arrangement has an inlet and an outlet connected in flow communication with an external source of a secondary coolant fluid, separate from the reactor coolant water and separate from the purge fluid, which then flows through the jacket over the set of coils contained therein. The secondary coolant fluid is typically at a temperature much lower than the temperature of the internal coolant fluid circulating about the closed path such that the heat carded by the internal coolant fluid gained from cooling the motor and bearings is readily transferred to the secondary coolant fluid through the one set of coils in the jacket.
A drawback of this type of heat removal arrangement is that it increases the complexity of the cleanup pump.
It has been proposed in the past to use the purge fluid system as a heat removal means where an intermittent flow of purge fluid is delivered into the cleanup pump. However, this idea had not been fully developed and, therefore, was never utilized.
There remains, therefore, a need for providing a more simple, less complicated way for cooling an electrical motor and bearings of a nuclear reactor water cleanup pump of a boiling water reactor.
This and other needs are satisfied by the present invention.